1. Technical Field
The present invention relates to a quantum interference device, an atomic oscillator, an electronic apparatus, and a moving object.
2. Related Art
As for an oscillator which has a high accuracy oscillation characteristic for a long period of time, an atomic oscillator is known which oscillates on the basis of energy transition of atoms of an alkali metal such as rubidium or cesium (for example, refer to JP-A-2009-164331).
Generally, operation principles of the atomic oscillator are largely classified into a method of using a double resonance phenomenon caused by light and microwaves, and a method of using a quantum interference effect (also referred to as coherent population trapping (CPT)) caused by two types of light beams with different wavelengths. Anatomic oscillator using the quantum interference effect can be made smaller-sized than an atomic oscillator using the double resonance phenomenon, and thus has been recently expected to be mounted in various apparatuses.
The atomic oscillator using the quantum interference effect, as disclosed in JP-A-2009-164331, includes a gas cell into which gaseous metal atoms are sealed; a semiconductor laser which irradiates the metal atoms in the gas cell with laser light including two types of resonance light beams having different frequencies; and a light detector which detects the laser light which has been transmitted through the gas cell. In such an atomic oscillator, when a frequency difference between the two types of resonance light beams matches a specific value, neither of the two types of resonance light beams is absorbed by the metal atoms in the gas cell and are transmitted. This is called an electromagnetically induced transparency (EIT) phenomenon, and an EIT signal which rapidly increases due to the EIT phenomenon is detected by the light detector.
Here, from the viewpoint of increasing detection accuracy of the light detector, the EIT signal preferably has a small line width (half width). Therefore, a coil which generates a magnetic field in a direction along an optical axis of laser light is provided in the gas cell. By providing the coil, gaps between degenerated other energy levels of the atoms of the alkali metal in the gas cell are enlarged by the Zeeman splitting, and thus resolution can be improved. Therefore, it is possible to reduce a line width of the EIT signal.
In order to improve stability of a magnetic field in the gas cell, the gas cell and the coil are stored in a shield case (for example, refer to JP-A-2010-287937 and JP-A-2009-302118). JP-A-2010-287937 does not disclose a specific method of forming the shield case. On the other hand, JP-A-2009-302118 discloses that the shield case is formed by folding a sheet metal. However, if the sheet metal is only folded, a thickness of the shield case cannot be sufficiently secured at a part where edges of the sheet metal are close to or come into contact with each other. For this reason, there is a problem in that a shield effect of the shield case decreases.